Pathological stimuli alter the transcriptional program of the heart, thereby contributing to the pathogenesis of cardiac hypertrophy and failure. This transcriptional program is profoundly influenced by chromatin structure, which changes dynamically in response to extracellular cues. Cardiac gene expression is also controlled by a set of key transcription factors, including GATA4, which is essential for cardiac hypertrophy. Chromatin structure regulates transcription factor binding to DNA, and conversely transcription factors recruit protein complexes that modify chromatin structure. However, little information is available about this complex interplay between chromatin structure and transcription factors, particularly in the context of cardiac gene expression and the pathogenesis of heart failure. We and others have shown that GATA4 is an essential regulator of adult heart function. In our preliminary data, we further show that the GATA4 cofactor FOG2 is essential for normal function of the adult heart, in part by maintaining the coronary vasculature. In addition, we demonstrate a novel interaction between GATA4 and the polycomb complex PRC2, which governs cellular differentiation and lineage commitment by catalyzing histone methylation. In this proposal, we test the broad hypothesis that GATA4- chromatin interactions regulate the transcription of GATA4 target genes in cardiac hypertrophy and failure, and these interactions are modulated by FOG2 and PRC2. We propose the following specific aims: (1). In a neonatal cardiomyocyte hypertrophy model, we test the hypothesis that hypertrophic stimulation alters GATA4 chromatin occupancy and induces GATA4-dependent changes in chromatin structure that drive altered gene expression in cardiac hypertrophy. (2). We identify genes regulated by FOG2-GATA4 that contribute to the heart failure phenotype of FOG2-deficient mice, and dissect molecular mechanisms by which FOG2 influences GATA4-dependent transcriptional of these genes. (3). We test the hypothesis that PRC2 is essential for cardiac hypertrophy and function, and investigate the functional significance of GATA4-PRC2 interaction in regulating cardiac growth and homeostasis. These aims will provide novel insights into how cellular context regulates transcriptional activity through interactions between transcription factors and chromatin structure. This knowledge may lead to novel therapeutic approaches for heart failure.